"..because in each circuit, the 4th gear switch is simply in series with solenoid..."

I see that in all 3 of your OD circuits. IMO that's key to the problem. It should be in the relay COIL circuit as with the 240 M46 OD.

Your OD 3 is close, and would work if the 4th GS was put in series with the Momentary Dashboard switch. That would make a logical "AND" of both switches be required for relay (and thus solenoid) control. Re-engaging 4th would not power the solenoid until the momentary PB switch was pushed again.

That's essentially what I suggested, except that the OD momentary switch is on the + side of the coil while the 4th GS is in the coil ground side. And the later "electronic latching" relay, eliminates the older mechanical type.

Thinking further on it, I believe both later style Auto OD relays can be wired to work also, and would be more readily available at the Man's Mall for the DIY'er. Post back if you want the details.
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.